Modern double-hung and casement windows are typically mounted in an aluminium or vinyl outer frame or jamb, on a pivot mechanism that provides means for both sliding the window sash relative to the outer frame and tilting the window sash out of the plane of the frame. This facilitates easier assembly of the window sash to the frame, and cleaning of the window after installation.
In a typical sliding/pivoting window construction, the window sash is mounted at one end on opposed pivot pins which are disposed in sliding shoes, each shoe being respectively trapped in a channel formed in the outer frame. This allows the window sash to slide along the frame within the plane of the frame like a sliding window, or to be pivoted out of the plane of the frame like a pivoting window. This provides considerable versatility in the positioning of the window within the frame by a user.
It is advantageous, both for safety reasons and to facilitate cleaning of the window, that when the window sash is pivoted out of the plane of the frame the window sash be prevented from sliding along the frame. Accordingly, it is known to provide a sliding shoe which can be expanded to lock against the channel in the window frame. For example, U.S. Pat. No. 5,168,665 issued Dec. 8, 1992 to Goldenberg, which is incorporated herein by reference, teaches a sliding pivot shoe assembly having a body with a split end and a cam disposed in the body adjacent to the split end. When the cam is rotated, the body expands to engage the sides of the channel in the frame. The window sash is pivotally mounted on the cam by a pivot pin keyed to the cam, so that when the window sash is pivoted out of the plane of the frame the cam rotates and the shoe body frictionally locks into position in the channel.
However, there are different mechanisms used to bias the window sash to a closed position in the frame, by to biasing the shoe to an end of the channel, and prior art sliding shoes are not adapted to be used with these various different mechanisms. Furthermore, because the prior art sliding shoes are of a unitary construction, the cam is not trapped in the shoe and can become displaced when the sash pivot is mounted into the cam, and the shoe can expand only in the lateral direction, relying solely on the sides of the shoe to engage the sides of the channel. Also, in prior art shoes the spreading action occurs very slowly in the rotational cycle of the cam, and thus the window locks into position in the frame only when the window sash is pivoted almost completely out of the plane of the frame, which is undesirable. The faster the shoe gets into the lock position, the less chance the sash has to move while locking.